I'm for gay-marriage personally, for a number of reasons, even though I am straight myself.
However, I have one friend who is deeply Catholic and he brought to my attention a major problem with the idea of religious marriage and gay people in his view: marriage is a sacrament in his and some other religions. Simplified that means it's a holy thing that a holy person engages people in with the blessing and authority of their mutual god in under a specific, religiously determined, set of parameters - some of those being prohibitive of people of the same sex receiving it.
That's a problem because no authority outside of the religion can confer that and no authority from outside of the religion can alter those parameters.
Now, there are non-religious marriage equivalents that already exist. Atheists can get married, two people from different religions can get married, people who are not particularly looking to do anything more than tie their legal lives together can get married, using these means. So, it's marriage still, but has a diminished or no religious component. They can have whatever ceremonies they like, but there is no official religious blessing involved in such cases. Fine and well. I think gay people can and should have the same options. And all of those are still called marriage - because that is what they are, the semantics issue is a non-issue for those groups, so it should be a non-issue for gay marriages I think.
If gay people want weddings within whatever religion they belong to, then they are going to have to, from within the religion, change the parameters of receiving that sacrament, and unfortunately outside help is not going to do much for that situation, as it is entirely an inside thing.
What can be done and should be done, in my opinion, is the governmental option of civil unions (which will be called marriages, because that is what they are and claiming a word... well that's a whole different discussion about language - words are symbols they mean what we all think and agree that they mean and that is constantly changing and evolving and it isn't a determined thing it's a dynamic shared thing - language is descriptive, not prescriptive - things don't mean what the dictionary tells us they mean, dictionaries catalog what we've decided words mean) in non-religious terms so that the rights and legal protections are the same for two men getting married as a man and a woman atheist getting married as a man and a woman of different religious backgrounds getting married, as a two women getting married, as a man and a woman of the same religion getting married, and so on and so on. Legally and socially these things should all be the same. Because they are the same. And people will talk about them like they are the same, using the same word, because it is convenient, which is what words are for - making description of concepts and things and places convenient for more rapid verbal and written communication.